230 



SCIENCE 



[N. S. Vol. XXVIII. No. 712 



This being the case it will be evident 

 that the effective portion of the work of 

 any introduced parasite lies within the 

 fraction of one per cent, that would other- 

 wise survive. It therefore follows that 

 should an insect be introduced that would 

 destroy fifty per cent, of the pest, more 

 than forty-nine per cent, of this fifty per 

 cent, is simply the destruction of indi- 

 viduals that would have died from other 

 causes. The real question to be settled 

 therefore becomes whether the new insect 

 replaces a more or a less efficient cause of 

 death. The apparent per cent, of efficiency 

 is really no criterion whatever of the value 

 of the introduction. That which we are 

 desiring to secure is the reduction of the 

 numbers especially during the period of 

 injury, and therefore the only significant 

 datum is the determination of the relative 

 abundance maintained by the injurious 

 species. The numbers of any particular 

 parasite is not even a safe index of its 

 role in the maintenance of this status, un- 

 less one were able to accurately weigh its 

 eificiency as contrasted with that which it 

 replaced. 



All entomologists appreciate that natural 

 enemies are largely if not the only con- 

 trolling factors that maintain the present 

 status of insect abundance, but do not so 

 uniformly appreciate that the change of 

 status though related is nevertheless essen- 

 tially a different problem. 



C. W. Wood WORTH 



IjNivEBSirr OF California 



AN ASTRONOMICAL EXPEDITION TO 

 ARGENTINA 



The Department of Meridian Astrometry 

 of the Carnegie Institution, in charge of 

 Professor Lewis Boss of the Dudley Ob- 

 boll weevil the extreme annual migration is about 

 the width of two counties. The total extension 

 of this insect into new territory only requires an 

 average survival of about two per cent, in the 

 outer two tiers of counties. 



servatory at Albany, N. Y., where the work 

 of the department is carried on, is dis- 

 patching an expedition to the Argentine 

 Republic to establish a branch observatory 

 there. This observatory will be established 

 at San Luis about 500 miles west from 

 Buenos Aires. This town of about 10,000 

 inhabitants is located near the eastern edge 

 of the Andean plateau at an elevation of 

 about 2,500 feet. It is reported to have a 

 fine climate with remarkably clear skies. 



The new observing station consists of 

 the necessary observing structures, and 

 temporary barracks for office rooms and 

 quarters for the staff. The principal in- 

 strument will be the Olcott Meridian Circle 

 of the Dudley Observatory. This instru- 

 ment will be set up in its new location for 

 the purpose of making reciprocal observa- 

 tions upon stars already observed at 

 Albany, together with observations upon 

 all stars from south declination to the 

 south pole that are brighter than the 

 seventh magnitude, or which are included 

 in Laeaille 's extensive survey of the south- 

 ern stars made at the Cape of Good Hope 

 in 1750. It is thought that this new 

 scheme of making reciprocal observations 

 on the same stars, with the same instru- 

 ment, alternately used in the two hemis- 

 pheres will present peculiar advantages in 

 point of accuracy in the systematic sense. 

 To reach this accuracy has long been the 

 problem of fundamental work in astron- 

 omy. It is estimated that the work of 

 observation in Argentina will last three or 

 four years. 



The object of these observations is to 

 gather material for facilitating the con- 

 struction of a general catalogue of about 

 25,000 stars, in which will be contained ac- 

 curately computed positions and motions 

 of all the stars included in it. 



The department has already completed 

 for publication a general catalogue of 6,188 

 stars, including all the most accixrately ob- 



